Jay T. Snyder, P.G., P.E., C.Hg.
EA Engineering, Science and Technology, Inc.
Jay Snyder is a Professional Engineer, Professional Geologist, and Professional Hydrologist-Groundwater (AIH) with over 28 years of experience in soil and groundwater corrective action, serving a variety of federal, state, and commercial clients. He has directed hundreds of hydrogeologic investigations, field-scale pilot tests, remedial alternative evaluations and remedial action plans at LUST sites, RCRA facilities, Superfund sites, mine sites and oil and gas facilities. He specializes in risk-based corrective action at hydrocarbon contaminated sites, remedial investigations at hazardous waste sites, and evaluation and specification of remedial alternatives at a wide variety of sites contaminated with fuels, solvents, metals, creosote and agricultural wastes. He has applied a wide variety of remedial technologies, including groundwater pump and treat, air sparging, multiphase extraction, in situ thermal desorption, soil vapor extraction, in situ bioremediation, monitored natural attenuation, land farming, chemical oxidation, and permeable reactive barriers. He has prepared permits for numerous remediation systems, including appropriation of groundwater right, Class V injection well permits, groundwater discharge plans, and New Source Review for air emissions.He currently serves as hydrogeology technical lead for EA’s EPA RAC contracts in Region 6 and Region 9, and Air Force cleanups at Eielson, Hill and Kirtland Air Force Bases.
PLATFORM PRESENTER – Biological Treatment: Strength in Small Packages
Field Scale Pilot Study of Chromium Reduction and ERD in a Declared Aquifer
A field scale pilot test was performed to address groundwater contamination at an NPL site in Texas. Sources areas associated with the groundwater plume include unlined floor sumps, disposal sumps, surface spills and leaks, and sludge drainage from unlined lagoons. These discharges have resulted in a hexavalent chromium solute plume measuring 900 feet by 300 feet, consisting of “yellow” groundwater with concentrations in the hundreds of mg/L. Commingled with the chromium plume is a trichloroethene (TCE) plume with maximum concentrations of 1 to 2 mg/L, 400 feet wide by 1,400 feet long. The groundwater contamination occurs in a Texas Water Development Board declared minor aquifer, which is used as a water supply source locally; however, no water wells are located nearby.
The pilot test consisted of injecting two separate carbon electron donors in two different areas with high concentrations of chrome and TCE. In each area, a fully penetrating injection well was installed with two downgradient observation points. The observation points consisted of nested 5 foot screens separated by bentonite seals in a common borehole, and fully penetrating observation wells.
In one area, electron donor was depleted before the hexavalent chromium was fully reduced. However, at the second test site, hexavalent chromium was fully reduced and enhanced reductive dechlorination (ERD) ensued, resulting in dechlorination of TCE to dichloroethene, and on to vinyl chloride.
Over the course of the pilot test, hexavalent chromium apparently had to be completely reduced before the oxidation-reduction potential of the aquifer could drop to levels conducive to ERD of TCE. The effect of unwanted electron acceptors, such as nitrate and sulfate, on loading rates of carbon substrate amendments with in situ bioremediation (ISB) via ERD is well understood. However, the effect of reducible metals in groundwater, such as hexavalent chromium, on the required loading rates (and tangentially on redox conditions) of carbon substrate amendments to promote ERD is poorly understood.
This study provides field evidence that dissolved hexavalent chromium may delay the establishment of optimal redox conditions that promote ERD of TCE. The establishment of strongly negative ORP conditions in groundwater was delayed until after hexavalent chromium was mostly reduced in groundwater, and because initial chromium concentrations were high, chromium reduction did not occur for several months. This observation suggests that oxidation of the substrate amendment is first paired with chromium reduction, delaying the accumulation of sufficient hydrogen by fermentation to create optimal redox conditions for ERD of TCE. This is supported by the lack of ERD at the test location where the substrate amendment was depleted prior to complete chromium reduction.
Based on the second test site, ISB using the second test amendment to promote chromium reduction and ERD was the selected remedy for groundwater contamination. Other deductions and recommendations for further study are offered in this paper to further the industry’s understanding of the influence of reducible metals on carbon substrate loading rates and the establishment of optimal redox conditions for ERD.
CO-AUTHORS: Jay Snyder, PG, PE, EA Engineering, Science and Technology, Inc.; Frank Barranco, PhD, PE, PG, EA Engineering, Science and Technology, Inc.; Kenneth Min, EA Engineering, Science and Technology, Inc.; Samantha Saalfield, PhD, EA Engineering, Science and Technology, Inc.
Biosparging Pilot Test in Confined Aquifer
A confined aquifer biosparging pilot test was performed at the Former Laguna Mart, Laguna Pueblo, New Mexico. In 2003 14,000 cubic yards of contaminated soil were excavated. Although the source was removed, residual contamination in a deep confined aquifer continued to contaminant groundwater. Assessment of this contamination revealed two contaminated water bearing zones: (1) the water table, and (2) a deeper zone beneath a two-foot thick clay aquitard where black stained residual NAPL was encountered, having migrated to this position during historically lower groundwater levels resulting from local pumping.
The pilot test was conducted to evaluate biosparging a confined aquifer, a practice generally discouraged in guidance. However, innovative vent wells that allow sparge air to bubble above the confining layer facilitate the process under confined conditions.
Test wells included sparge points installed 20 feet below the confining layer, vent wells screened immediately below the confining layer, and existing site wells. Sparge points facilitated air injection, and deep monitoring wells, existing wells, and vent wells provided observation points.
Pressure/flowrate response testing was stepped, with the following results in the two sparge wells: pressure stepped from 23 psig to 25.5 psig resulted in flowrate increase from 1 scfm to 2.5 scfm in one well, and in the other, stepping from 10.5 and 19.5 psig resulted in flowrate increase from 0.75 scfm to 2 scfm. A flow rate of less than 2 scfm was sufficient to volatilize contaminants and raise groundwater dissolved oxygen levels. During deep sparging, no change in oxygen and carbon dioxide levels was in the shallow SVE system indicating no communication.
During biosparge testing, substantial increases in PID concentrations were observed in all but one observation well. Increases pre- and post sparge increased from 12 to 1,815; 2.7 to 660 ppmv; 1 to 79 ppmv, 7 to 675 ppmv, 10 to 1,867 ppmv, 1.7 to 515 ppmv; and 2.7 to 551 ppmv. Only a couple wells did not respond positively, indicating limited anisotropy.
Carbon dioxide (CO2) concentrations varied over time, but generally decreased as intial CO2 was stripped and a sustained mineralize rate achieved. Carbon dioxide concentration increase is attribute to effects of in-situ aerobic biodegradation (mineralization) of gasoline constituents. Dissolved oxygen (DO) concentrations increased in four wells, but decreased in two. Changes were noted within four hours of sparging. DO increases include 0.51 to 3.01, 0.79 to 5.06, 0.85 to 1.14, and 5.4 to 6.7 mg/L.
Design parameters obtained include radius of air sparge influence as far as 25 feet, initial short term emission rate of 0.0.075 lb/hr per scfm, and sparge pressure of 25 to 30 psig. A mass removal/destruction rate of approximately 14,500 pounds per year was estimated based on air stripping and In Situ Bioremediation based on oxygen delivery. The pilot test demonstrated the viability of sparging a confining aquifer. The Remedial Design was completed and the system installed. Operation phase is pending. System consists of over 90 vent and sparge wells in water table and confined aquifer.
CO-AUTHORS: Jay Snyder, PG, PE, EA Engineering, Science and Technology, Inc.; Vener Mustafin, PE, EA Engineering, Science and Technology, Inc.; Tyler Curley, PE, EA Engineering, Science and Technology, Inc.